For the reception and for the regeneration of optical signals after they have passed through a transmission system, digital optical receivers are known which comprise an analog input part, in which the optical signal is converted into an analog electrical signal, and a digital signal processing part, in which the analog signal is regenerated into a digital data signal having a normalized amplitude and clock information. In the analog part, the optical signal received is converted into a photocurrent by means of a photodiode and amplified in a preamplifier.
It is known practice, in digital optical receivers of this type or even in another context, to carry out signal detection (signal detect). Signal detection allows the threshold value detection of a particular optical power level at the input of the receiver. It is used to indicate the presence of a signal having a particular optical power level. This information may be used to control, for example activate or deactivate, the optical receiver and other system components. Signal detection provides a logic “signal detect” signal, which has the logic value ONE (when a signal of a particular optical power level is present) or the logic value zero (if a signal of this type is not present).
Signal detection usually works by absolute-value formation or rectification and monitoring of the peak value of the input signal and comparison thereof with a reference value. To this end, it is known practice to carry out signal detection with the aid of mixers, source and emitter followers, respectively, as rectifiers. This is disadvantageously associated with a considerable area requirement and current consumption.